Bulletproof batteries could soon be used as armour for soldiers. Lumping military kit around on foot is a tiresome job, with batteries accounting for as much as a quarter of the weight they have to carry. But if they doubled up as armour too that could drastically lighten the load. The average soldier is carrying roughly twenty pounds (9 Kg) of body armour and eighteen pounds (8 kg) of batteries in the field, says Gabriel Veith at Oak Ridge National Laboratory in Tennessee. If we could integrate the two we could reduce the total weight on the soldier. So far, Veiths team has managed to make small bullet proof batteries by incorporating silica nanoparticles into the batterys electrolyte, a liquid that allows for the flow of charge. The addition means the electrolyte becomes rigid on impact, a process known as shear-thickening. Normally the slight repulsive force between particles in the electrolyte allows them to flow past each other, but shock overcomes this force and the particles lock together to behave like a solid, which should be strong enough to stop a bullet. Adding the silica nanoparticles only adds about 3 per cent to the total weight of the battery. The military already have wearable battery packs, but these offer no protection, and are a liability if damaged as they can catch fire, explode or vent toxic gases. The US Air Force want wearable batteries that can stop handgun bullets and aim to produce an effective design over the next year, followed by the construction of prototypes. The technology could also make electric vehicles better able to withstand impacts. While tests have been successful with small batteries, Veith says there are still challenges to overcome when scaling up. One of these is manufacture: normally liquid electrolyte is injected into the battery, but this is not possible with a shear-thickening liquid which stiffens. The idea of using shear-thickening fluids as impact protection in the batteries of electric vehicles is really clever, says Helen Wilson at University College London, but warns there may be engineering challenges. Extending the technology further to create wearable batteries as armour might be too much of a stretch, she says.
New Scientist, 24 May 2018 ; http://www.newscientist.com/